18S6.] DR. OtJNTHER ON A FIERASFER IN A PEART.-OYSTER. 319 



Tlie specimen, which is represented in the accompanying woodcut 

 of the natural size, has been in my jjossession for many years. It 

 is an old shell of Maryarita maryaritifera, in which there is im- 

 bedded, behind the impression of the attractor mnscle, a perfect 



individual of a fish belonging to the genus Fierasfer. The fish is 

 coTcred by a tliin layer of pearl-substance, through which not only 

 the general outlines of the body but even the eye and the mouth can 

 be seen. The parasitic habits of Fierasfer are well known, and 

 Putnam describes, in the ' Proceedings of the Boston Society of 

 Natural History,' vol. xvi. 18/4, p. 344, a species, Fierasfer dulius, 

 which is found on both coasts of Central America, but inhabits 

 Holothurians on the Atlantic, and Pearl-Oysters on the Pacific side ; 

 and he further mentions, in a footnote, an example belonging to the 



